Abstract:

Background/Aims: Amyloid imaging is poised to enter the clinical arena, yet few studies have examined its impact on clinical diagnosis and management. We evaluated the longitudinal course and clinical decision making in patients seen at our Center who had a PIB result that was discordant with the pre-scan clinical diagnosis.
Methods: 69 of clinically diagnosed AD patients were PIB-negative (8.7%), and/65 patients with frontotemporal lobar degeneration (FTLD), a non-Aβ dementia, were PIB-positive (13.8%). Median follow up was visits (range-10) over years (range-11). The clinical course of these patients was retrospectively reviewed by a neurologist and neuropsychologist to assess: (1) longitudinal evolution; (2) change in clinical diagnosis after release of PIB results; (3) changes in prescribed medications.
Results: PIB-negative AD:Two patients showed little cognitive change, and the diagnosis was changed to MCI due to psychiatric and vascular causes. Three patients evolved an FTLD syndrome (PSP, PPA) and clinical diagnosis was changed appropriately. One patient continued to show progressive amnesia with relative sparing of other domains, and the diagnosis remained AD. No changes in medications occurred related to PIB results. PIB-positive FTLD: Four PPA patients (two non-fluent variant and two semantic variant) showed PIB uptake despite typical disease courses. Even though diagnosis was unchanged, cholinesterase inhibitors were added in three cases. Five FTD patients had a positive PIB, which together with their clinical evolution prompted a change in diagnosis to AD. In three cases cholinesterase inhibitors were added.
Discussion: The clinical trajectories of patients with discordant PIB results varied and suggested: (1) non-degenerative cognitive impairment; (2) possibly incidental AD pathology in patients with classical FTLD syndromes; (3) misclassification of AD vs. FTLD. Clinical diagnosis was often affected by PIB results, particularly in PIB-negative AD. Cholinesterase inhibitor treatment was initiated in most patients that were unexpectedly PIB-positive.